On my terminal in Ubuntu, I often run programs which keep running for a long time. And since there are a lot of these programs, I keep forgetting which terminal is for which program, unless I tab through all of those. So I wanted to find a way to update my terminal title to the program name, whenever I run a command. I don't want to do it manually.

I use gnome-terminal, but answer shouldn't really depend on that. Basically, If I'm able to run a second command, then I can simply use gconftool command to update t开发者_如何学运维he title. So I was hoping to find a way to capture the command in bash and update the title after every command. How do I do that?

I have some answers for you :) You're right that it shouldn't matter that you're using gnome-terminal, but it does matter what command shell you're using. This is a lot easier in zsh, but in what follows I'm going to assume you're using bash, and that it's a fairly recent version (> 3.1).

First of all:

Which environment variable would contain the current 'command'?

There is an environment variable which has more-or-less what you want - $BASH_COMMAND. There's only one small hitch, which is that it will only show you the last command in a pipe. I'm not 100% sure what it will do with combinations of subshells, either :)

So I was hoping to find a way to capture the command in bash and update the title after every command.

I've been thinking about this, and now that I understand what you want to do, I realized the real problem is that you need to update the title before every command. This means that the $PROMPT_COMMAND and $PS1 environment variables are out as possible solutions, since they're only executed after the command returns.

In bash, the only way I can think of to achieve what you want is to (ab)use the DEBUG SIGNAL. So here's a solution -- stick this at the end of your .bashrc:

trap 'printf "\033]0;%s\007" "${BASH_COMMAND//[^[:print:]]/}"' DEBUG

To get around the problem with pipes, I've been messing around with this:

function settitle () {
    export PREV_COMMAND=${PREV_COMMAND}${@}
    printf "\033]0;%s\007" "${BASH_COMMAND//[^[:print:]]/}"
    export PREV_COMMAND=${PREV_COMMAND}' | '
}

export PROMPT_COMMAND=${PROMPT_COMMAND}';export PREV_COMMAND=""'

trap 'settitle "$BASH_COMMAND"' DEBUG

but I don't promise it's perfect!

Try this:

trap 'echo -ne "\033]2;$(history 1 | sed "s/^[ ]*[0-9]*[ ]*//g")\007"' DEBUG

Thanks to the history 1 it works even with complicated expressions like:

true && (false); echo $? | cat

For which approaches relying on $BASH_COMMAND or $@ fail. For example simon's displays:

true | echo $? | cat

Thanks to Gilles and simon for providing inspiration.

I see what stoutie is trying to do, except it's a lot more work than needed. And doesn't cause all sorts of other potentially bad things that can occur as a result of redefining 'cd' and putting in all of that testing just to change directories. Bash has built in support for most of this.

You can put this in your .bashrc anywhere after you set your current PS1 prompt (this way it just prepends it)

# If this is an xterm set the titlebar to user@host:dir
case "$TERM" in
xterm*|rxvt*)
    PS1="\[\e]0;\u@\h: \w\a\]$PS1"
    ;;
*)
    ;;
esac

The OP asked for bash, but others might be interested to learn that (as mentioned above) this is indeed a lot easier using the zsh shell. Example:

# Set window title to command just before running it.
preexec() { printf "\x1b]0;%s\x07" "$1"; }

# Set window title to current working directory after returning from a command.
precmd() { printf "\x1b]0;%s\x07" "$PWD" }

In preexec, $1 contains the command as typed (requires shell history to be enabled, which seems to be a fair assumption), $2 the expanded command (shell aliases etc.) and $3 the "very expanded" command (shell function bodies). (more)

I'm doing something like this, to show my pwd in the title, which could be modified to do whatever you want to do with the title:

function title { echo -en "\033]2;$1\007"; }
function cd { dir=$1; if [ -z "$dir" ]; then dir=~; fi; builtin cd "$dir" && title `pwd`; }

I just threw this in my ~/.bash_aliases.

Update

I ran into strange bugs with my original answer. I ended up picking apart the default Ubuntu PS1 and breaking it into parts only to realize one of the parts was the title:

# simple prompt
COLOR_YELLOW_BOLD="\[\033[1;33m\]"
COLOR_DEFAULT="\[\033[0m\]"
TITLE="\[\e]0;\u@\h:\w\a\]"
PROMPT="\w\n$ "
HUH="${debian_chroot:+($debian_chroot)}"
PS1="${COLOR_YELLOW_BOLD}${TITLE}${HUH}${PROMPT}${COLOR_DEFAULT}"

Without breaking into variables, it would look like this:

PS1="\[\033[1;33m\]\[\e]0;\u@\h:\w\a\]${debian_chroot:+($debian_chroot)}\w\n$ \[\033[0m\]"

I have tested three method, all is OK, use any one for your pleasure.

export PROMPT_COMMAND='echo -ne "\033]2;$(history 1 | sed "s/^[ ]*[0-9]*[ ]*//g")\007"'

trap 'echo -ne "\033]2;$(history 1 | sed "s/^[ ]*[0-9]*[ ]*//g")\007"' DEBUG

trap 'echo -ne "\e]0;"; echo -n $BASH_COMMAND; echo -ne "\a"' DEBUG

please note if use $BASH_COMMAND, it don't recognize bash alias, and use PROMPT_COMMAND show finished command, but use trap show running command.

Based on the the need to auto position putty windows I have modified my /etc/bash.bashrc file on a Debian/Ubuntu system. I have posted the full contents for completeness but the relevant bit to starts on the # Display command ... comment line.

# System-wide .bashrc file for interactive bash(1) shells.

# To enable the settings / commands in this file for login shells as well,
# this file has to be sourced in /etc/profile.

# If not running interactively, don't do anything
[ -z "$PS1" ] && return

# check the window size after each command and, if necessary,
# update the values of LINES and COLUMNS.
shopt -s checkwinsize

# set variable identifying the chroot you work in (used in the prompt below)
if [ -z "${debian_chroot:-}" ] && [ -r /etc/debian_chroot ]; then
    debian_chroot=$(cat /etc/debian_chroot)
fi

# set a fancy prompt (non-color, overwrite the one in /etc/profile)
PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '

# Display command run in title which allows us to distinguish Kitty/Putty
# windows and re-position easily using AutoSizer window utility. Based on a
# post here: http://mg.pov.lt/blog/bash-prompt.html
case "$TERM" in
xterm*|rxvt*)
    # Show the currently running command in the terminal title:
    # http://www.davidpashley.com/articles/xterm-titles-with-bash.html
    show_command_in_title_bar()
    {
        case "$BASH_COMMAND" in
            *\033]0*)
                # The command is trying to set the title bar as well;
                # this is most likely the execution of $PROMPT_COMMAND.
                # In any case nested escapes confuse the terminal, so don't
                # output them.
                ;;
            *)
                echo -ne "\033]0;${USER}@${HOSTNAME}: ${BASH_COMMAND}\007"
                ;;
        esac
    }
    trap show_command_in_title_bar DEBUG
    ;;
*)
    ;;
esac

# Commented out, don't overwrite xterm -T "title" -n "icontitle" by default.
# If this is an xterm set the title to user@host:dir
#case "$TERM" in
#xterm*|rxvt*)
#    PROMPT_COMMAND='echo -ne "\033]0;${USER}@${HOSTNAME}: ${PWD}\007"'
#    ;;
#*)
#    ;;
#esac

# enable bash completion in interactive shells
if ! shopt -oq posix; then
  if [ -f /usr/share/bash-completion/bash_completion ]; then
    . /usr/share/bash-completion/bash_completion
  elif [ -f /etc/bash_completion ]; then
    . /etc/bash_completion
  fi
fi

# if the command-not-found package is installed, use it
if [ -x /usr/lib/command-not-found -o -x /usr/share/command-not-found/command-not-found ]; then
        function command_not_found_handle {
                # check because c-n-f could've been removed in the meantime
                if [ -x /usr/lib/command-not-found ]; then
                   /usr/bin/python /usr/lib/command-not-found -- "$1"
                   return $?
                elif [ -x /usr/share/command-not-found/command-not-found ]; then
                   /usr/bin/python /usr/share/command-not-found/command-not-found -- "$1"
                   return $?
                else
                   printf "%s: command not found\n" "$1" >&2
                   return 127
                fi
        }
fi

You can set up bash such that it sends a certain escape sequence to the terminal every time it starts an external program. If you use the escape sequence that terminals use to update their titles, your problem should be solved.

I have used that before, so I know it is possible. but I cannot remember it off the top of my head and do not have time to research the details right now, though.

Some of the old methods were removed from gnome-terminal 3.14 due to these two bugs (724110 and 740188).

In Ubuntu 20.04

PS1=$PS1"\[\e]0;New_Terminal_Name\a\]"

\[ begin a sequence of non-printing characters

\e]0; is the char sequence for setting the terminal title. Bash identifies this sequence and set the tile with the following characters. Number 0 turns out to be the value to reference the title property.

New_Terminal_Name is the tile we gave

\a is the ASCII bell character, also in this case, it marks the end of the tile to read from Bash.

\] end a sequence of non-printing characters

We can create a function for future use

function set_title(){
 if [ -z "$PS1_BACK" ];  # set backup if it is empty
 then
  PS1_BACK="$PS1"
 fi

 TITLE="\[\e]0;$*\a\]"
 PS1="${PS1_BACK}${TITLE}"
}

Open the ~/.bashrc file in your home directory with a text editor and append the above function at the end of it. Save and close.

To use it immediately source it to the current terminal.

source ~/.bashrc

We can use it then like this

set_title <New terminal tab title>

My terminal window titler script

This dynamic backgrounded script show all running command with pid number and elapsed time in seconds, like if I run du -h | less, this will build title looking like:

204640 6 du -h | 204641 6 less

Then when no command (other than himself) are running, don't change the terminal title, so standard behaviours works normaly.

First run start backgroud task. Second run in same terminal ask for kill previous backgrounded task.

Save this into a file, set execute flag then run it without argument:

cat <<"EOF" >titleWin.sh

#!/bin/bash

## Ask for kill process if already started
mapfile -t pids < <(ps -C ${0##*/} ho pid)
for pid in ${pids[@]} ;do
    if [[ $pid != $$ ]] && [ -d /proc/$pid ]; then
    echo -n "STARTED: [$pid]: ${0##*/}. Kill them (Y/n)? "
    read -rsn 1 act
    case $act in
        n|N ) echo No;;
        * ) echo Yes;kill $pid ;;
    esac
    exit
    fi
done

## Title win for xterm or screen (or tmux).
case $TERM in
    xterm*|rxvt* ) titleFmt='\e];%s\a';;
    screen* ) titleFmt='\ek%s\e\\';;
    * ) echo "Unable to title window.";exit 1;;
esac
tty=$(tty)

## Date to epochseconds converter
exec {dateout}<> <(:)
exec {datein}> >(exec stdbuf -o0 date -f - +%s >&$dateout)
DPID=$!
trap "echo TRAP;kill $DPID" 1 2 3 6 9 15

# Main loop 
while :;do
    string=""
    while read -r pid wday mon day time year cmd; do
        if [[ $pid != $$ ]] && [[ $pid != $PPID ]] && [[ $pid != $BASHPID ]] &&
               [[ $pid != $DPID ]] && [ "${cmd#*pid,lstart,cmd}" ] &&
               [ -d /proc/$pid ] ;then
            echo >&${datein} $wday $mon $day $time $year
            read -ru $dateout date
            string+="$pid $((EPOCHSECONDS-date)) $cmd | "
        fi
    done < <(exec ps --tty ${tty#*/dev/} ho pid,lstart,cmd)
    [[ "$string" ]] && printf "$titleFmt" "${string% | }"
    sleep .333
done &

EOF

chmod +x titleWin.sh

./titleWin.sh